There are already known push-piece winding button control devices. European Patent No EP1930794, for example, describes a magnetic push-piece winding button control device for timepieces. According to this document, the push-piece winding button control stem has a profiled section which is essentially formed of two grooves and one inclined part. The profiled section is arranged to cooperate with the two arms of a split elastic ring in order to index the position of the push-piece winding button control stem by holding or returning the latter in or to a selected axial position. The control stem, which is symmetrical with respect to a determined plane passing through a longitudinal axis, is free to rotate between the two arms of the split elastic ring. By pressing or pulling out the push-piece winding button, the wearer of the watch can choose to make the control stem occupy three different, predefined positions. A stable first position, called the rest position, in which the arms of the split elastic ring are engaged in a first groove; a stable second position, called the pulled-out position, in which the arms of the split elastic ring are engaged in a second groove; and finally a transitory position, called the pushed-in position, in which the arms of the split elastic ring cooperate with the inclined part of the profiled section, such that, under the combined action of the pressure from the arms of the split elastic ring on the inclined part of the inclined section and the return force exerted by a spring, the control stem returns to the rest position as soon as the wearer of the watch releases pressure on the push-piece winding button.
Implementing a push-piece winding button control device like the one just described above is not, however, without a certain number of problems. In particular, one drawback lies in the fact that, in order to machine the cam path in a section of the control stem, the diameter of the control stem must be relatively large, which makes the use of such a control stem quite difficult, or even impossible, particularly in the field of wristwatches, where it is undesirable to have to machine large diameter holes in the case middle for passage of a control stem, in particular due to the thickness of the case middle.
Another example of such a control stem is illustrated in FIG. 22, annexed to this Patent Application. Designated as a whole by the general reference numeral 200, this control stem includes a cylindrical portion 202 terminating with a push-piece winding button 204 at its end located outside the portable object (not represented) which is fitted with it. Towards its end opposite to push-piece winding button 204, cylindrical portion 202 of control stem 200 is provided with a cam path 206 formed of three successive annular grooves 208a, 208b and 208c separated from each other by two flanges 210a and 210b of substantially rounded profile. The dimensions of annular grooves 208a-208c are adapted to those of the elastic arms 212 of a spring 214, for example, a U-shaped spring, which projects, for example, into annular groove 208a of cam path 206. It is understood that, in order to make elastic arms 212 of spring 214 move from annular groove 208a into annular groove 208b, the user must exert on control stem 200 a traction force greater than the force necessary for elastic arms 212 to move apart and slide over flange 210a before closing again on annular groove 208b. Conversely, if it is desired to move elastic arms 212 of spring 214 from annular groove 208b into annular groove 208a, a thrust force must be exerted on control stem 200 sufficient to enable elastic arms 212 to deform and cross flange 210a and drop into annular groove 208a. The same applies to the transition of elastic arms 212 of spring 214 from annular groove 208b into annular groove 208c and vice versa.
Thus, through cooperation between the elastic arms of a spring and a cam path which is integral with the cylindrical portion of a control stem, it is advantageously possible to define, for example, three stable positions of the control stem which each correspond to the setting of a given function. The drawback of this solution lies, however, in the fact that, in order to machine the cam path in the cylindrical portion of the control stem, the diameter of the cylindrical portion of the control stem must be relatively large, which makes the use of such a control stem quite difficult, or even impossible, especially in the field of wristwatches, where it is undesirable to have to machine large diameter holes in the case middle, in particular due to the thickness of the case middle.